Bacterial Reduction of Toxic Hexavalent Chromium and its Application to Biological Treatment of Waste Waters

六价铬（CrO_4<2->）对大多数生物体具有毒性和致突变性。在许多工业过程中产生含有有毒铬酸盐的废水沃茨。我们从活性污泥中分离出一株铬酸盐还原菌，鉴定为阴沟肠杆菌。还原态铬（Cr 3+）的毒性比铬酸盐小得多，在中性条件下易形成不溶性的铬氢氧化物。研究了该菌还原铬酸盐的能力，并将其用于沃茨中有毒铬的解毒和去除。其还原动力学的重要特征是：（1）还原速率与菌体密度成正比;（2）高浓度的铬酸盐对还原有抑制作用，（3）在10- 30 ℃范围内，温度对还原的影响符合Arrhenius方程，（4）还原发生在pH6.5和8.5之间，（5）还原速率与碳源和能源的添加量有关，（6）还原速率与碳源和能源的添加量有关。（6）铬酸盐的还原对氧胁迫敏感，但当氧胁迫解除后，铬酸盐的还原又迅速恢复。Clobacillus菌株HO 1可还原受污染的工业废水中的有毒铬酸盐。铬酸盐的还原需要碳源和能源。其它金属离子如Cu^2+、Mn^2+、Zn^2+等对铬酸盐还原有一定的抑制作用。可以说，有可能建立一种成本有效的方法来从污染的沃茨中去除有毒的铬酸盐。

Hexavalent chromiun (chromate : CrO_4^<2->) is toxic and mutagenic for most organisms. Waste waters containing toxic chromate are generated in many industrial processes. We have isolated a chromate-reducing bacterium, identified as Enterobacter cloacae, from activated sludge. Reduced chromium (Cr^<3+>), which is much less toxic than chromate, readily formed insoluble chromium hydroxides at a neutral pH. The ability of this bacterium to reduce chromate was examined for detoxification and removal of toxic chromium from waste waters.The important features of the reduction kinetics were : (1) the rate of reduction was proportional to cell density ; (2) high concentrations of chromate inhibited the reduction ; (3) the effect of temperature followed the Arrhenius equation over the temperature range of 10-30C ; (4) the reduction occurred at pH6.5 and 8.5 ; (5) the reduction rate was dependent on the amount of added carbon and energy sources ; (6) the reduction of chromate was sensitive to oxygen stress, but when released from the oxygen stress, it readily resumed.E. cloacae strain HOl could reduce toxic chromate in a contaminated industrial effluent. Carbon and energy sources were required for the reduction of chromate. Chromate reduction was inhibited to some extent by other metal ions including Cu^<2+>, Mn^<2+> and Zn^<2+>.This method requires neither high energy nor chemical reagents. It can be said that there is a potential for establishing a cost effective method to remove toxic chromate from contaminated waters.